Efficient cqi signaling in multi-beam mimo systems

ABSTRACT

The present invention relates to the signaling of channel quality information in a multi-beam transmission system, wherein a plurality of beams are simultaneously transmitted and a plurality of sets of channel quality information are transmitted for controlling independently the transmission rate on the different beams. Determined are beams with a different quality resulting in different effects of errors in the transmissions of the channel quality information for the beams. Said different effects are exploited for reducing a signaling overhead of the channel quality information for the beams.

The present application is a continuation of U.S. patent applicationSer. No. 14/055,975, filed on Oct. 17, 2013, (to be issued as U.S. Pat.No. 9,154,200 on Oct. 6, 2015) which is a continuation of U.S. patentapplication Ser. No. 12/438,158, filed on Feb. 20,2009, now issued asU.S. Pat. No. 8,588,116 on Nov. 19, 2013, which was the National Stageof International Application No. PCT/IB2007/053284 filed on Aug. 17,2007, which claims priority of EP applications EP06119254 filed Aug. 21,2006, and EP06119326 filed Aug. 22, 2006, each of which are incorporatedby reference herein in their entirety.

The present invention relates to a method for signaling channel qualityinformation in a multi-beam transmission system, in particular amulti-beam MIMO (multiple-in/multiple-out) system. Moreover, the presentinvention relates to a computer program product for carrying out themethod. Further, the present invention relates to a multi-beamtransmission system, in particular a multi-beam MIMO system, wherein aplurality of beams are simultaneously transmitted and a plurality ofsets of channel quality information (CQI) are transmitted forcontrolling independently the transmission rate on the different beams.Still further, the present invention relates to a network element, inparticular a node, in a multi-beam transmission system, in particular amulti-beam MIMO system, wherein a plurality of beams are simultaneouslytransmitted and a plurality of sets of channel quality information aretransmitted for controlling independently the transmission rate on thedifferent beams. Still further, the present invention relates to a userequipment, in particular a mobile station, in a multi-beam transmissionsystem, in particular a multi-beam MIMO system, wherein a plurality ofbeams are simultaneously transmitted and a plurality of sets of channelquality information are transmitted for controlling independently thetransmission rate on the different beams. Finally, the present inventionrelates to a signal for indicating channel quality information in amulti-beam transmission system, in particular a multi-beam MIMO system,wherein a plurality of beams are simultaneously transmitted and aplurality of sets of channel quality information are transmitted forcontrolling independently the transmission rate on the different beams.

The present invention can be applied in multi-antenna communicationsystems. In particular, a potential application of the present inventionis in the MIMO feature currently being standardized for UMTS (universalmobile telecommunication system) Release 7.

In the third generation partnership project (3GPP) a proposal calledD-TxAA is under discussion for UMTS as a way of increasing the peak bitrate. This is derived from an existing closed loop transmit diversityscheme (TxAA mode 1) where the mobile terminal signals to the networkcomplex weights which should be applied to the signals from each of twotransmitting antennas. In D-TxAA two different data streams aretransmitted using orthogonal weight vectors, wherein a first weightvector is based on those transmitted from the mobile terminal, and asecond vector is derived deterministically from the first vector.

For the operation of D-TxAA, the following may be assumed:

Orthogonal pilot channels are transmitted from an antenna of each Node B(which is a logical node responsible for radio transmission andreception in one or more cells to and from an user equipment (UE).

No dedicated (i.e. beam formed) pilots are available (assuming that thefractional dedicated physical channel (F-DPCH) is used, which does notcarry pilot bits).

Feedback information (FBI) for the first beam is derived by the userequipment (UE) and transmitted to Node B, indicating the desiredbeamforming vector.

The first beam is transmitted using a restricted codebook of weightvectors (for example the codebook currently used for TxAA mode 1).

The identity of the antenna weight vector for a first beam is signaledto the UE on the High-Speed Shared Control Channel (HS-SCCH).

The second beam is transmitted using a deterministic phase vector, whichis orthonormal to the vector for the first beam.

Channel quality information (CQI) is signaled by the UE to the Node B,enabling the Node B to derive a different rate for each of the twobeams.

The CQI indicates the rate (or packet size) which can be transmittedsuccessfully (or with a given probability of success) using a referencepower level and code resource (the reference values being known by boththe network and the mobile terminal).

The transmissions on the two beams are comprised of separate codewordswith potentially different rates.

As the simultaneously transmitted beams in D-TxAA are typically receivedwith different SINR (signal-to-noise ratio where the noise includes boththermal noise and interference) at the UE, each beam can support acorrespondingly different rate. This implies that multiple CQIinformation is required to be signaled to the Node B by each UE. In UMTSRelease 5, a single CQI value is comprised of 5 information bits, codedinto 20 physical channel bits. For a multiple-beam system, this numberof bits would be multiplied by the number of beams if a separate CQIvalue is indicated for every beam. This can result in a high signalingload.

An object of the present invention is to reduce the CQI signaling loadin multi-beam systems.

In order to achieve the above and further objects, in accordance with afirst aspect of the present invention, there is provided a method forsignaling channel quality information in a multi-beam transmissionsystem, in particular a multi-beam MIMO system, wherein a plurality ofbeams are simultaneously transmitted and a plurality of sets of channelquality information are transmitted for controlling independently thetransmission rate on the different beams, comprising the steps ofdetermining beams with different quality, and exploiting said differentqualities for reducing a signaling overhead of the channel qualityinformation for the beams.

In accordance with a second aspect of the present invention, there isprovided a computer program for carrying out the method according to thefirst aspect of the present invention.

In accordance with a third aspect of the present invention, there isprovided a multi-beam transmission system, in particular a multi-beamMIMO system, wherein a plurality of beams are simultaneously transmittedand a plurality of sets of channel quality information are transmittedfor controlling independently the transmission rate on the differentbeams, comprising a determining device for determining beams withdifferent quality, and an exploiting device for exploiting saiddifferent qualities for reducing a signaling overhead of the channelquality information for the beams.

In accordance with a fourth aspect of the present invention, there isprovided a network element, in particular a node, in a multi-beamtransmission system, in particular a multi-beam MIMO system, wherein aplurality of beams are simultaneously transmitted and a plurality ofsets of channel quality information are transmitted for controllingindependently the transmission rate on the different beams, comprising adetermining device for determining beams with different quality, and anexploiting device for exploiting said different qualities for reducing asignaling overhead of the channel quality information for the beams.

In accordance with a fifth aspect of the present invention, there isprovided a user equipment, in particular a mobile station, in amulti-beam transmission system, in particular a multi-beam MIMO system,wherein a plurality of beams are simultaneously transmitted and aplurality of sets of channel quality information are transmitted forcontrolling independently the transmission rate on the different beams,comprising a determining device for determining beams with differentquality, and an exploiting device for exploiting said differentqualities for reducing a signaling overhead of the channel qualityinformation for the beams.

In accordance with a sixth aspect of the present invention, there isprovided a signal for indicating channel quality information in amulti-beam transmission system, in particular a multi-beam MIMO system,wherein a plurality of beams are simultaneously transmitted and aplurality of sets of channel quality information are transmitted forcontrolling independently the transmission rate on the different beams,the signal comprising a reduced overhead of channel quality informationfor the beams, based on exploiting differences in qualities of thebeams.

The present invention leads to a reduction of the CQI signaling load inmulti-beam transmission systems. This advantage is achieved inparticular by that according to the present invention the differenteffects of errors in the CQI transmissions for the different beams whicheffects result from different quality of the beams are exploited forusing signaling overhead of CQI for the multiple beams.

Further advantageous embodiments are defined in the dependent claims.

Preferably, said determining device is adapted to determine beams withdifferent quality resulting in different effects of errors in thetransmissions of the channel quality information for the beams, and inparticular said determining device is adapted to determine a primarybeam with a higher quality and at least one secondary beam with a lowerquality in the plurality of beams resulting in different effects oferrors in the channel quality information transmissions for thesecondary beam(s).

There may be a differential signaling device for providing adifferential signaling for indicating the channel quality informationvalue for the secondary beam(s). The differential signaling device maybe adapted to signal an absolute value of the channel qualityinformation for the primary beam, and the channel quality informationvalues for the secondary beam(s) by means of an offset relative to thevalue for the primary beam. Further, the differential signaling devicemay be adapted to derive the offset from an average difference inquality between the respective secondary beam and the primary beam.

Preferably, the exploiting device may be adapted to provide differentupdate rates for the channel quality information for different beams,wherein the differential signaling device may be adapted to signal theoffset at a lower update rate than the absolute channel qualityinformation value for the primary beam. Further, the exploiting devicemay be adapted to provide a lower update rate for the channel qualityinformation transmissions relating to the secondary beam(s) compared tothe update rate for the channel quality information transmissionsrelating to the primary beam. The update rates may be signaled from anetwork element, in particular a node, to a user equipment, and may bepredetermined.

Preferably, the exploiting device is adapted to provide differentcut-off thresholds, below which a reporting of channel qualityinformation is not required, for different beams, and in particular theexploiting device is adapted to provide a higher cut-off threshold forthe secondary beam(s) than for the primary beam. The cut-off thresholdsmay be signaled from a network element, in particular a node, to a userequipment, and may be predetermined Further, scheduled time instants areprovided for the user equipment to transmit channel quality informationto the network element, and when user equipment estimates that thechannel quality for a beam is below the respective cut-off threshold forthat beam, the user equipment does not transmit channel qualityinformation at the scheduled time instants until the channel quality isabove the respective cut-off threshold. Moreover, according to apreferred embodiment, wherein when the network element does not receivechannel quality information at a scheduled time instant it does not makeany further transmissions on the respective beam(s) until it receives adifferent channel quality information value from the user equipment.

Preferably, the exploiting device is adapted to provide differentchannel quality information quantization granularities for differentbeams. The exploiting device may be adapted to provide a coarser channelquality information quantization granularity for the secondary beam(s)compared to the channel quality information quantization granularityapplied to the channel quality information reports for the primary beam.Further, the exploiting device may be adapted to apply the coarserchannel quality information quantization granularity for the secondarybeam(s) only to a lower part of the channel quality information range. Anetwork element, in particular a node, may be provided to instruct auser equipment to use different channel quality information quantizationgranularities for different beams. Still further, the channel qualityinformation quantization granularities may be predetermined.

Preferably, an encoding device is provided for jointly encoding thechannel quality information values transmitted for more than one beaminto a single codeword for transmission from a user equipment to anetwork element, in particular a node.

It is recognized that in D-TxAA systems a first beam is typically alwaysof better quality than a second beam as the beam forming weights for thefirst beam are specifically designed to optimize thesignal-to-interference ratio (SIR) of the first beam, while the beamforming weights for the second beam are derived deterministically fromthe first beam.

In general, multi-beam transmission systems can be considered to becomprised of a primary beam with an optimized SIR and one or moresecondary beams with a lower SIR.

Consequently, the effect of errors in the CQI signaling for thesecondary beam(s) is considered to be less significant than the effectof errors in the CQI signaling for the primary beam, when consideringthe total achievable transmission rate over all the beams. This resultsin a different effect of errors in the CQI transmissions for thesecondary beam(s).

Therefore, at first, a primary beam and one or more secondary beams aredetermined among the multiple beams.

Then, the different effects of errors in the CQI transmissions for thesecondary beam(s) are exploited for reducing a signaling overhead of CQIfor the multiple beams.

Preferably, the exploiting of the different effects can include one ormore of the following three measures or steps:

-   1. A different (typically lower) update rate is provided for the CQI    transmissions relating to at least one secondary beam compared to    the update rate for the CQI transmissions relating to the primary    beam. These update rates are signaled to the UE by the Node B. In a    typical embodiment, a rate of CQI reporting is signaled for the    primary beam, and one or more further (advantageously lower) update    rates are signaled for one or more secondary beams. In some    embodiments, the one or more further update rates may be signaled by    means of a divisor of the rate signaled for the primary beam. In a    variation of this embodiment, the update rate for CQI transmissions    is optionally selected depending upon the rate of change of the    channel on each beam.-   2. A different (typically higher) cut-off threshold is provided for    one or more beams, below which the UE should not report CQI values    for the respective beams. In the prior art, an “out-of-range” CQI    value is provided for transmission by the UE when the SIR is too low    for the UE successfully to decode any of the available transmission    formats. However, transmission of such a value continues to    contribute to an uplink signaling overhead, even when no data can be    received on the downlink. In order to reduce the signaling overhead,    the Node B signals to the UE a cut-off CQI level for one or more    beams, below which the UE ceases to report CQI for that beam, and    the Node B makes no further transmissions on such beams until it    receives from the UE another CQI value. In a variation of this    embodiment particularly suited to cases where a fixed number of bits    is allocated in the uplink signaling channel for CQI reporting    purposes, the proportion of the fixed number of uplink bits    available for CQI reports is varied according to beam quality, such    that when one or more beams have an “out of range” CQI and hence no    CQI report is sent, more CQI bits for the “in range” beam(s) may be    sent instead to improve their quantization and/or reliability.-   3. A different (typically coarser) CQI quantization granularity is    provided for at least one secondary beam compared to the CQI    quantization granularity applied to the CQI reports for the primary    beam. If the rate of the secondary beam(s) is lower and therefore    the total rate is less sensitive to errors in the CQI for the    secondary beam(s), it is more efficient to coarsen the granularity    of the CQI reporting for those beams whereby the number of required    signaling bits is reduced. For example, while a 1 dB granularity is    typically applied for a primary beam, the Node B might use signaling    to instruct the UE to use a coarser granularity (e.g. 2 dB) for one    or more secondary beams. Alternatively, the granularities could be    predetermined in the specification. In a further embodiment, the    coarser granularity for a secondary beam could apply only to a lower    part of the CQI range. In a variation of this embodiment, the range    of CQI values to be transmitted for the secondary beam(s) may be    different from the range of CQI values to be transmitted for the    primary beam; the granularity for each beam may optionally then be    the same. For example, the total range of possible CQI values could    be split into a number of sub-ranges, and a UE would signal only a    CQI value within a beam's current sub-range. In an extension of this    embodiment, special CQI values could be reserved to indicate    switching up or down to the next sub-range of CQI values. Sub-ranges    might further be designed to overlap, or be extended or reduced or    otherwise adapted by further signaling in order to optimize them for    the current beams and channel conditions.

In any of the embodiments, the CQI values transmitted for more than onebeam can be jointly encoded into a single codeword for transmission tothe Node B.

Differential signaling may be used to indicate the CQI value for one ormore secondary beams. For example, an absolute value of CQI may besignaled for the primary beam, and the CQI values for one or moresecondary beams may be signaled by means of an offset relative to thevalue for the primary beam. In particular, the offset can be signaled ata lower update rate than the absolute CQI value for the primary beam. Infurther embodiments, the offset can be derived from an averagedifference in quality between the respective secondary beam and theprimary beam, wherein the averaging period can be e.g. related to theupdate rate of the primary beam CQI value, related to the update rate ofthe offset, predetermined, signaled to the UE by the Node B, or signaledto the Node B by the UE.

Such a difference in CQI may be in terms of a transmission power offsetwhich is required between a secondary beam and the primary beam,assuming that both beams would be transmitted with the same modulationand coding scheme. Alternatively the difference in CQI may be in termsof a transmission power offset required under the assumption that thesecondary beam is transmitted with a fixed difference (or ratio) in thedata rate relative to the primary beam.

Differential signaling for CQI is typically advantageous if the CQIvalues of different beams are correlated to a certain extent. In avariation of the embodiments using differential signaling, the UEtherefore measures and subtracts the correlated part of the CQI valuesof the different beams and transmits only a value relating to thenon-correlated part of the CQI for secondary beam(s) relative to aprimary beam. The period over which the correlation is measured can beselected in a similar way to the averaging period.

Although the invention has been described primarily in relation totransmissions from base stations to mobile terminals, the invention isalso applicable to transmissions from mobile terminals to base stations,and between peer nodes.

In the present specification and claims the word “a” or “an” precedingan element does not exclude the presence of a plurality of suchelements. Further, the word “comprising” does not exclude the presenceof other elements or steps than those listed.

From reading the present disclosure, other modifications will beapparent to persons skilled in the art. Such modifications may involveother features which are already known in the art of radio communicationand which may be used instead of or in addition to features alreadydescribed herein.

1. A method for signaling channel quality information in a multi-beam transmission system wherein a plurality of beams are simultaneously transmitted and one or more sets of channel quality information are transmitted for independently controlling the transmission rate on at least two of the plurality of beams, the method comprising: in a network element: determining a received signal-to-interference ratio (SIR) of the at least two beams of the plurality of beams; determining a first beam of the at least two beams of the plurality of beams to be a primary beam as a consequence of the determined received signal-to-interference ratio (SIR) being not less than a received SIR of any other beam of the at least two beams of the plurality of beams; determining at least one other beam of the least two beams of the plurality of beams to be a secondary beam; and reducing a signaling overhead of the channel quality information (CQI) for the at least two beams of the plurality beams by providing different reporting rates for the channel quality information (CQI) for the primary beam and the at least one secondary beam wherein providing different reporting rates for the channel quality information (CQI) comprises providing a lower reporting rate for (CQI) transmissions relating to the at least one secondary beam compared to a reporting rate for the (CQI) transmissions relating to the primary beam.
 2. A non-transitory computer-readable storage medium having stored thereon instructions that when executed cause processing circuitry of a network element in a multi-beam transmission system to: in a network element: determine a received signal-to-interference ratio (SIR) of the at least two beams of the plurality of beams; determine a first beam of the at least two beams of the plurality of beams to be a primary beam as a consequence of the determined received signal-to-interference ratio (SIR) being not less than a received SIR of any other beam of the at least two beams of the plurality of beams; determine at least one secondary beam of the least two beams of the plurality of beams; and reduce a signaling overhead of the channel quality information (CQI) for the at least two beams of the plurality beams by providing different reporting rates for the channel quality information (CQI) for the primary beam and the at least one secondary beam.
 3. A network element in a multi-beam transmission system, the network element comprising: a determining device for determining a received signal-to-interference ratio (SIR) of at least two beams of a plurality of beams in a multi-beam transmission system; the determining device for determining a first beam of the at least two beams of the plurality of beams to be a primary beam as a consequence of the determined received signal-to-interference ratio (SIR) being not less than a received SIR of any other beam of the at least two beams of the plurality of beams; the determining device for determining at least one other beam of the least two beams of the plurality of beams to be a secondary beam; and a reducing device for reducing a signaling overhead of the channel quality information (CQI) for the at least two beams of the plurality beams by providing different reporting rates for the channel quality information (CQI) for the primary beam and the at least one secondary beam.
 4. A base station in a multi-beam transmission system, the base station comprising: a determining device for determining a received signal-to-interference ratio (SIR) of at least two beams of a plurality of beams in a multi-beam transmission system; the determining device for determining a first beam of the at least two beams of the plurality of beams to be a primary beam as a consequence of the determined received signal-to-interference ratio (SIR) being not less than a received SIR of any other beam of the at least two beams of the plurality of beams; the determining device for determining at least one other beam of the least two beams of the plurality of beams to be a secondary beam; and a reducing device for reducing a signaling overhead of the channel quality information (CQI) for the at least two beams of the plurality beams by providing different reporting rates for the channel quality information (CQI) for the primary beam and the at least one secondary beam.
 5. The base station according to claim 4, wherein providing different reporting rates for the channel quality information (CQI) comprises providing a lower reporting rate for (CQI) transmissions relating to the at least one secondary beam compared to reporting rate for the (CQI) transmissions relating to the primary beam.
 6. The base station according to claim 4, wherein a differential signaling is used to indicate the channel quality information value for the at least one secondary beam.
 7. The base station according to claim 6, wherein an absolute value of the channel quality information (CQI) is signaled for the primary beam, and the channel quality information values for the at least one secondary beam are signaled as an offset relative to the absolute value for the primary beam.
 8. The base station according to claim 7, wherein the offset is derived from an average difference in channel quality between the respective at least one secondary beam and the primary beam.
 9. The base station according to claim 7, wherein the offset is signaled at a lower reporting rate than the reporting rate for the absolute channel quality information for the primary beam.
 10. The base station according to claim 9, wherein the channel quality information (CQI) transmissions are signaled at a lower reporting rate for the at least one secondary beam relative to the reporting rate for the channel quality information (CQI) transmissions the primary beam.
 11. The base station according to claim 9, wherein the reporting rates are signaled from the network element to the user equipment (UE).
 12. The base station according to claim 9, wherein the reporting rates are predetermined.
 13. The base station according to claim 4, wherein different cut-off thresholds of channel quality are provided for the different beams, the different cut-off thresholds defining a level below which a reporting of channel quality information (CQI) is not required.
 14. The base station according to claim 13, wherein a higher cut-off threshold is provided for the at least one secondary beam than for the primary beam.
 15. The base station according to claim 14, wherein when the user equipment estimates that the channel quality for a beam is below the respective cut-off threshold for that beam, the user equipment does not transmit channel quality information at the scheduled time instants until the channel quality is above the respective cut-off threshold.
 16. The base station according to claim 15, wherein the different cut-off thresholds are signaled from the network element, to the user equipment (UE).
 17. The base station according to claim 15, wherein the cut-off thresholds are predetermined.
 18. The base station according to claim 15, wherein scheduled time instants are provided for the user equipment to transmit channel quality information (CQI) to the network element.
 19. The base station according to claim 15, wherein when the network element does not receive channel quality information at a scheduled time instant it does not make any further transmissions on the different beams until it receives a different channel quality information value from the user equipment.
 20. The base station according to claim 4, wherein different channel quality information quantization granularities are provided for the different beams.
 21. The base station according to claim 4, wherein a coarser channel quality information quantization granularity is provided for the at least one secondary beam compared to the channel quality information quantization granularity applied to the channel quality information (CQI) reports for the primary beam.
 22. The base station according to claim 21, wherein the coarser channel quality information quantization granularity for the at least one secondary beam only applies to a lower part of the channel quality information range.
 23. The base station according to claim 21, wherein the network element instructs the user equipment to use different channel quality information quantization granularities for different beams.
 24. The base station according to claim 21, wherein the channel quality information quantization granularities are predetermined.
 25. The base station according to claim 4, wherein the channel quality information values transmitted for more than one beam are jointly encoded into a single codeword for transmission from a user equipment to a network element.
 26. A user equipment, in a multi-beam transmission system, the user equipment comprising: a determining device for determining a received signal-to-interference ratio (SIR) of at least two beams of a plurality of beams in a multi-beam transmission system; the determining device for determining a first beam of the at least two beams of the plurality of beams to be a primary beam as a consequence of the determined received signal-to-interference ratio (SIR) being not less than a received SIR of any other beam of the at least two beams of the plurality of beams; the determining device for determining at least one other beam of the least two beams of the plurality of beams to be a secondary beam; and a reducing device for reducing a signaling overhead of the channel quality information (CQI) for the at least two beams of the plurality beams by providing different reporting rates for the channel quality information (CQI) for the primary beam and the at least one secondary beam.
 27. The user equipment according to claim 26, wherein providing different report rates for the channel quality information (CQI) comprises providing a lower reporting rate for (CQI) transmissions relating to the at least one secondary beam compared to a reporting report rate for the (CQI) transmissions relating to the primary beam.
 28. The user equipment according to claim 26, wherein a differential signaling is used to indicate the channel quality information value for the at least one secondary beam.
 29. The user equipment according to claim 28, wherein an absolute value of the channel quality information (CQI) is signaled for the primary beam, and the channel quality information values for the at least one secondary beam are signaled as an offset relative to the absolute value for the primary beam.
 30. The user equipment according to claim 29, wherein the offset is derived from an average difference in channel quality between the respective at least one secondary beam and the primary beam.
 31. The user equipment according to claim 30, wherein the offset is signaled at a lower reporting rate than the reporting rate for the absolute channel quality information value for the primary beam.
 32. The user equipment according to claim 31, wherein the channel quality information (CQI) transmissions are signaled at a lower reporting rate for the at least one secondary beam relative to the reporting rate for the channel quality information (CQI) transmissions the primary beam.
 33. The user equipment according to claim 31, wherein the reporting rates are signaled from the network element to the user equipment (UE).
 34. The user equipment according to claim 31, wherein the reporting rates are predetermined.
 35. The user equipment according to claim 26, wherein different cut-off thresholds of channel quality are provided for the different beams, the different cut-off thresholds defining a level below which a reporting of channel quality information (CQI) is not required.
 36. The user equipment according to claim 27, wherein a higher cut-off threshold is provided for the at least one secondary beam than for the primary beam.
 37. The user equipment according to claim 36, wherein when the user equipment estimates that the channel quality for a beam is below the respective cut-off threshold for that beam, the user equipment does not transmit channel quality information at the scheduled time instants until the channel quality is above the respective cut-off threshold.
 38. The user equipment according to claim 37, wherein the different cut-off thresholds are signaled from the network element, to the user equipment (UE).
 39. The user equipment according to claim 37, wherein the cut-off thresholds are predetermined.
 40. The user equipment according to claim 37, wherein scheduled time instants are provided for the user equipment to transmit channel quality information (CQI) to the network element.
 41. The user equipment according to claim 37, wherein when the network element does not receive channel quality information at a scheduled time instant it does not make any further transmissions on the different beams until it receives a different channel quality information value from the user equipment.
 42. The user equipment according to claim 26, wherein different channel quality information quantization granularities are provided for the different beams.
 43. The user equipment according to claim 26, wherein a coarser channel quality information quantization granularity is provided for the at least one secondary beam compared to the channel quality information quantization granularity applied to the channel quality information (CQI) reports for the primary beam.
 44. The user equipment according to claim 43, wherein the coarser channel quality information quantization granularity for the at least one secondary beam only applies to a lower part of the channel quality information range.
 45. The user equipment according to claim 43, wherein the network element instructs the user equipment to use different channel quality information quantization granularities for different beams.
 46. The user equipment according to claim 43, wherein the channel quality information quantization granularities are predetermined.
 47. The user equipment according to claim 26, wherein the channel quality information values transmitted for more than one beam are jointly encoded into a single codeword for transmission from a user equipment to a network element. 